This invention pertains generally to rechargeable batteries and specifically to rechargeable nickel-zinc batteries. More specifically, this invention pertains electrode assemblies used in rechargeable nickel-zinc batteries and methods of manufacture.
The popularity of cordless portable devices, such as power tools, has increased the needs and requirements for high energy density rechargeable batteries that can also deliver high power. As power and energy density requirements increase, the need for a high cycle life rechargeable electrodes also increases. The alkaline zinc electrode is known for its high voltage, low equivalent weight and low cost. The fast electrochemical kinetics associated with the charge and discharge process enables the zinc electrode to deliver both high power and high energy density. Nickel-zinc batteries can satisfy the need for higher power and higher energy density in e.g. batteries, suitable for electric vehicles (EV), plug-in hybrid electric vehicles (PHEV), consumer electronics and other applications.
Particularly important is life cycle of rechargeable batteries. Nickel-zinc batteries can suffer from electrical shorts due to, e.g., dendrite formation from the negative (zinc) electrode to the positive (nickel) electrode. Previous approaches to this problem include, e.g., chemical modification of the electrodes to reduce the propensity toward shorting, but these are not typically optimal chemistries for high rate discharge and battery capacity. Coating or taping edges of electrodes is difficult to implement on a production scale and typically are not highly effective.
Separators are typically used to block dendrites from creating shorts between the electrodes but dendrites can migrate around separators unless they are sealed to envelop the electrodes. Sealing separators to envelop individual electrodes effectively blocks dendrite growth (or other particle migration) between electrodes, which extends battery life. In prismatic cells individual electrodes are enveloped prior to assembly of the electrode stack.
In wound electrodes, enveloping individual electrodes prior to winding is problematic due to wrinkling, binding and other difficulties attributable to the physical characteristics of the separator materials and the fact that many layers are wound together in the jellyroll. Heat sealing separators post-winding is known, but such methods only address sealing both electrodes on one end of a wound jellyroll electrode assembly. These methods do not allow for flexibility in internal cell design which is often critical in ever changing uses for rechargeable nickel zinc cells.